Recently, vibration and noise control have become important parameters to improve since they are related to the comfort of everyone, either in private or working spaces for example, in motor vehicles. A variety of experimental techniques exists to determine damping. The quantification of the vibration damping of a material may typically be expressed by a numerical value called tangent delta (also called tan delta, tan δ, loss tangent or loss factor) which is defined as the ratio of the loss modulus (which relates to the material's viscous behavior and defines the energy dissipation ability of the material) to the storage modulus of the material (which relates to the elastic behavior of the material and defines the energy storage ability of the material). Tan δ may be measured according to a dynamic mechanical analysis test that measures the complex modulus of the material as a measure of the dissipation of external vibrational energy. Typical viscoelastic materials present a strong dependence over the temperature and frequency range in which they are used as demonstrated by the presence of different state regions in distinct temperature or frequency regions: the Glassy, the Transition, the Rubbery and the Flow Regions. The material presents the highest storage modulus and therefore very low damping level at the Glassy Region, while it shows the most rapid change in storage modulus in the Transition Region from the glassy to the rubbery state and thus it is in this region that the material possesses its highest level of damping performance. Tan δ typically shows a maximum peak in this region which also can be used to define the glass transition temperature of the material. In the rubbery state both the storage modulus and the loss factor obtain somewhat low values and vary more slowly with changes in temperature and frequency. In the Flow region where the material continues to soften with increasing temperature the loss factor can attain very high values. The variation of the storage modulus and loss factor of a typical viscoelastic material with frequency shows that the effect of increasing temperature on the storage modulus is similar to the effect of reducing frequency thus governed by a temperature-frequency super-position principle which can be used to transform the material properties from the temperature domain to the frequency domain and vice-versa. The greater the value of tan δ, the better the vibration and noise reduction.
Absorption into the material reduces the vibrational energy transmitted, for example, to a passenger, and the noise that comes. Materials which exhibit efficient vibration damping show a high conversion of vibrational energy into other forms of energy, such as heat, i.e. they have a high tan δ. Such materials have a wide range of applications where vibration and noise is of concern, such as for example as components of motor vehicles, commercial airplanes, aerospace, household appliances, computer hardware, recreation and sports, machines, power equipment, buildings or mechanical devices.
For many applications, efficient vibration damping is desired over a broad range of temperature. In the automotive industry for example, materials used to dampen noises and vibrations should have sufficient tan δ values in a temperature range lying from about −35 to 80° C.
Various vibration damping and noise reduction materials have been described in the literature. JP 2000327894 discloses unsaturated polyester resins constituent for vibration damping. The unsaturated polyester resin composition comprises unsaturated polyester, ethylenically unsaturated monomer and graft copolymer. The graft copolymer consists of segment (A) comprising a thermoplastic elastomer and segment (B) comprising (co)polymer of (meth)acrylate. The disclosed resins have tan δ values equal or superior to 0.014 at 25 and 30° C.
U.S. Pat. No. 4,859,523 discloses vibration damping polyurethane resins produced by the reaction of an aromatic polyester diol, an aliphatic polyester diol, a diisocyanate compound and a chain extender. Such resins are useful for providing a composite vibration damping steel plate comprising two metal plate layers and the layer of the viscoelastic resin sandwiched between the metal layers. Such resins are reported to have glass transition temperature and therefore expected maximum tan δ value at various temperatures between 0° C. to 70° C. Such resins are reported to have a vibration damping peak temperature between 60° C. and 120° C. as determined by sandwiching the resin between two steel plates at a frequency of vibration of 500 Hz.
U.S. Pat. No. 5,356,715 discloses linear, high molecular weight polymers having blocks of epoxy and polyester or polyether resins said to be useful for forming vibration damping composites in metal sandwich structures.
WO 2004/106052 discloses housings said to be suitable for the attenuation of sound. Such housings comprise a plurality of rigid polymer layers separated by flexible polymer layers, wherein the flexible polymer layer is made of a thermoplastic elastomer having a polybutylene terephthalate hard segment and a glycol soft segment.
JP 2000212317 discloses a foamed polyester sheet comprising a copolyester and JP 07216072 discloses polyether ester block copolymers said to show low-temperature high vibration damping performance. JP 061361064 discloses sheets for sound deadening consisting of thermoplastic copolymerized polyester. U.S. Pat. No. 4,942,219 discloses the use of an amorphous block copolyester resin for a composite vibration damping material. US 5814696 discloses a polyester resin comprising an aromatic polyester resin and a polyester block copolymer resin.
EP 1212374 discloses sound damping polyester compositions comprising isoprenoid rubber modifier and a polyester selected from the group of consisting of poly(ethylene terephthalate) (PET), poly(propylene terephthalate (PPT), poly(butylene terephthalate) (PBT), poly(ethylene naphthanoate) (PEN), poly(butylene naphthanoate) (PBN) and mixtures thereof. U.S. Pat. No. 6,849,684 and WO 2002/032998 disclose a molded composition of a noise damping material made of a blend of a soft thermoplastic polyether and a hard polyester resin reinforced with a fibrous or particulate filler.
A need remains for materials having good vibration dampening and noise reduction performance over extendable temperature range (e.g. from −35 and 80° C.).